The present invention relates generally to analog-to-digital converters for use with personal computers and more particularly to a self-contained signal processor device which is designed for connection to a personal computer through the parallel printer port.
The ability to monitor, record and respond to analog signals is valuable in many engineering, manufacturing, medical and control applications in which personal computers are also employed. The market for analog signal processors has led personal computer manufacturers and others to make analog-to-digital (A/D) chips or cards which can be installed within the frame of a personal computer. In such prior art A/D converter options, the cover of the computer is removed, a card is plugged into the PC bus and the personal computer operating software is modified to acquire and convert analog signals to digital form for processing. Alternatively, various dedicated analog signal acquisition, transfer and storage devices are available which can transfer A/D converted data to a computer via disk, modem or another means of serial communication.
Disadvantages of prior art systems for enabling personal computers to monitor analog signals include the inconvenience of having to open the personal computer and install the necessary chip or card, the cost of such cards and the technical expertise required by someone setting up the computer to process analog signals. High resolution analog-to-digital conversion cards, capable of twelve-bit or more resolution, generally cost over a thousand dollars. Many owners of personal computers are discouraged from installing analog monitoring capability by these obstacles.
There is a need, therefore, for a simpler, less expensive add-on device for personal computers which can be used by non-experts to accomplish high-resolution analog monitoring functions. In particular, there is a need for an easily installed analog-to-digital converter which can be programmed through a personal computer and which will respond both to instructions from the personal computer and to the analog signal being monitored. Personal computer owners also would benefit from the ability to directly monitor other external signals such as frequency signals and digital status signals and to initiate commands to external equipment. That would allow the computer to monitor the status of home or office equipment, record external system parameters and control or adjust external devices. Dedicated devices are often available to perform such tasks and computers are able to be adapted for such purposes, but no device has heretofore been available to readily expand a personal computer to perform monitoring and control functions by means of a self-contained plug-in device.
It is an object of the present invention to provide a self-contained signal processing means for connection between a parallel printer port of a personal computer and a printer which allows the personal computer to monitor external signals such as analog and frequency signals without the requirement that the computer be physically opened and additional circuitry and devices be installed.
It is another object of the invention to provide such a signal processing means which is capable of digitizing analog signals for ready retrieval by a personal computer through the parallel printer port.
It is another object of the invention to provide such a signal processor which can monitor external digital status signals and output digital control signals in response to program instructions from the personal computer.
Accordingly, a signal processing means is provided in accordance with the present invention for connection between a parallel printer port of a personal computer and a printer. The signal processor comprises a first data buffer in which data is stored, means responsive to an external signal for producing data containing information about the external signal and for transferring the data into the first data buffer. In the illustrative embodiment described below, the means responsive to an external signal is an voltage-to-frequency converter responsive to an external analog voltage signal. The signal processor further comprises a printer control means which interconnects the parallel printer port of the personal computer to an external printer when in a transparent mode and selectively blocks the connection to the external printer when in a nontransparent mode. Logic control means are also provided, coupled to the personal computer through the parallel printer port and responsive to instructions from the personal computer, for controlling the signal processing means. Instructions from the personal computer carried out by the logic control means include selectively enabling the transparent and nontransparent modes of the printer control means and transmitting data from the first buffer, which in the illustrative embodiment is the digitized analog signal, to the personal computer through the parallel printer port.
Additional functions carried out by the preferred embodiment of the signal processing means of the present invention include the monitoring of external digital status signals, which are transferred to the personal computer, and the outputting of digital control signals in response to instructions from the personal computer. The analog signal processor can incorporate either voltage-to-frequency or analog-to-digital converters as the analog monitoring device, depending on the speed requirements of the user and cost considerations.